Those big puppy dog eyes may be powerful in addition to just being cute. According to a recent study, they may actually affect human choice about which dogs to adopt. The researchers who conducted the study “Paedomorphic Facial Expressions Give Dogs a Selective Advantage” found that dogs whose facial expressions made them look more puppyish were adopted more quickly from shelters than dogs who did not show such facial expressions. (Paedomorphism is the retention of infantile or juvenile traits into adulthood.)

One of the most prominent paedomorphic features is large eyes relative to the size of the face. This trait can be enhanced by raising the eyebrows which makes the overall height and size of the eyes seem bigger. It was this action of eyebrow raising that was studied in the experiment.

A total of 27 dogs were a part of the study. To minimize variation in facial features, all of the dogs were of similar types: Staffordshire Bull Terriers, Mastiffs and mixed bull breeds. Dogs were filmed for 2 minutes and researchers recorded the number of eyebrow raises and tail wags that each dog performed as well as noting how much time the dog spent at the front of the kennel. Frequency of eyebrow raises was associated with shorter times until adoption. Specifically, dogs who raised their eyebrows 5 times during filming were adopted in an average of 50 days, those that performed 10 eyebrow raises were adopted in an average of 35 days, and dogs who did it 15 times had an average waiting time until adoption of only 28 days.

Interestingly, they found that amount of tail wagging and time at the front of the kennel were not strongly associated with time until being adopted even though such traits are typically considered favorable behavioral signs of friendliness. It would be interesting to know if the eyebrow raising behavior correlates with temperament and suitability as a pet or if it is a behavior that serves more strictly to encourage caregiving behavior in humans.

These results may shed light on the domestication of dogs. It has been proposed that the juvenile traits of dogs arose as a byproduct of selection against aggression. This line of reasoning claims that people chose to associate with the least aggressive canines, and that the evolution of puppyish features and behavior developed as an accidental consequence of those choices. Experiments support the idea that selecting against aggression does lead to the evolution of juvenile traits. However, this latest study suggests that the puppylike features themselves may have influenced which canines became closely associated with humans and that such features may have evolved earlier in the process of domestication than previously thought.